The invention relates to polyurethanes containing isocyanurate rings, and in particular to polyurethane foams containing isocyanurate rings, which are also referred to as polyisocyanurate foam. The invention also relates to the process of preparing polyisocyanurate foams.
Polyurethanes that contain isocyanurate rings incorporated into the polymer are generally prepared by reacting a polyisocyanate with a polyol under conditions that promote the trimerization of the polyisocyanate to form an isocyanuric-acid derivative.
A drawback of that method of preparation is that a considerable quantity of the expensive polyisocyanate entering the reaction is consumed in the formation of the isocyanurate rings.
This drawback can be obviated by employing as a reactant a polyol containing an isocyanurate ring, for instance, tris-beta-hydroxyethyl isocyanurate. However, this compound has a melting point of over 100.degree. C and, hence, is difficult to process. The reaction product of isocyanuric acid, formaldehyde and an amino alcohol containing a primary or secondary amino group has been proposed as an alternative reactant. The aforementioned reaction product is characterized by the inherent drawback that the amino groups incorporated into the polyol act as a catalyst for the reactions with isocyanates, so that choice of catalyst with respect to amount and type, as best suited to the processing conditions, is severely curtailed.
The object of the invention is the production of polyurethanes containing isocyanurate rings from cheap starting materials, in which the isocyanurate rings are not obtained by trimerization of polyisocyanates. In particular, the object is the preparation of polyurethane foam containing isocyanurate rings.